The mainland's top official on Hong Kong affairs warned yesterday that "external interference" in the city's affairs was totally unacceptable to Beijing - an apparent reference to Britain.

Zhang Dejiang made the comments to Beijing loyalists during talks in Shenzhen, a Liberal Party source reported.

He also said the 2017 chief executive election was not the "be-all and end-all" in the city's pursuit of universal suffrage.

Zhang, chairman of the National People's Congress, was speaking as pan-democratic leading lights Martin Lee Chu-ming and Anson Chan Fang On-sang concluded a week-long visit to Britain. While in London, the pair raised concerns about political reform with Deputy Prime Minister Nick Clegg.

Lee, asked if he thought Zhang's comment was aimed at them, said he thought the remark was "weird". Referring to the agreement that set out the terms of Hong Kong's 1997 return to Chinese sovereignty, he said: "Britain was one of the signatories of the Joint Declaration. How could Britain have no responsibility in Hong Kong affairs?"

The Liberal source said: "Zhang said there were foreign countries meddling in Hong Kong's affairs which would affect the city's prosperity and stability ... and this was unacceptable to Beijing." Zhang also insisted democratic development in Hong Kong should take place "step by step".

And he was quoted by Andrew Leung Kwan-yuen, of the Business and Professionals Alliance, as saying Beijing would not back down because of Occupy Central, which is threatening to paralyse the business district in its push for universal suffrage.

Dr Chan Kin-man, co-organiser of the Occupy movement, said: "Now Beijing says 2017 is only the starting point … then when can we finally achieve genuine universal suffrage?"

Democratic Party chairwoman Emily Lau Wai-hing said the model for a chief executive election could be improved after 2017, but the next poll must offer a genuine choice of candidates.